The present disclosure relates to vibration sensors for cryogenic pumps and cryogenic pumps including the same.
Cryogenic pumps are centrifugal pumps designed specifically for handling cryogenic fluids such as liquid natural gas (LNG), liquid petroleum gas (LPG), liquid ethylene, propylene, ethane, and like cold fluids. These pumps are oftentimes submersible and made to operate under extreme conditions compared to other process industries. For example, one of the more critical pieces of equipment in a liquid natural gas (LNG) terminal are the LNG pumps, which operates under cryogenic conditions of −161° C.
Depending on the particular application, these types of pumps may be of substantial size with typical column lengths of about 15 to about 20 feet (about 4.5 to about 6 meters) or more, and column diameters ranging up to about 3 feet (about 1 meter) or more. The pump is thus made up of several major components, each of which may weigh several hundred pounds, wherein the total weight of the pump can be in excess of about 10,000 to about 15,000 pounds (about 4,500 to about 6,800 kilograms) or more.
Although the cryogenic pump is considered to be a quite reliable since the pump is normally installed in a clean, non-corrosive environment and is not exposed to the atmosphere, preventive maintenance of cryogenic pumps is often practiced since most cryogenic fluids have very high containment requirements to avoid gas leaks to the atmosphere or spills. Many pumps are now supplied with vibration detection systems. These systems are normally in the form of an accelerometer mounted directly to the pump housings with the instrument cable going up and out of the vessel or tank in much the same way as the power cables. These systems can provide a vibration level for normal operation and can provide alarms if vibration levels exceed an alert set point. The vibration systems can also be a valuable tool for trouble shooting, by allowing spectrum analysis of the vibration, which can be used to identify faults or impending failure.
However, working in a cryogenic environment presents difficulties since many pump designs result in the vibration sensor being in exposed to the cryogenic conditions or in some cases parallel to the power cables feeding the pump motors contact with the flowing cryogenic liquid. Applicant has discovered that saturation of the accelerometer signal produced by the vibration sensor can occur leading to inaccurate monitoring even when employing a cryogenic-rated accelerometer.